A large number of industrial trucks are powered by a battery. This makes it possible to obtain a braking effect by operating the electric motor as a generator. However, this generally is insufficient. Therefore, it is known to arrange a brake, i.e. a brake disc or brake drum, on the shaft of the motor. It is common to configure such brakes as spring brakes in which an electromagnetic force is applied to keep the braking member out of engagement with the brake disc or brake drum and the spring performs the braking procedure when such electric activation is stopped. It is further known to support the actuation of the spring electromagnetically.
As an alternative or in addition, it is further known to provide one load-bearing wheel of the industrial truck with a brake. The brake can be actuated hydraulically as has been generally known for other vehicles for a long time. However, it is also imaginable to actuate the brake unit electromagnetically on a load-bearing wheel.
Efforts have been made for some time to actuate electromagnetic brake systems electrically. Therefore, the connection between a brake pedal and the brake unit, e.g. on the load-bearing wheel, is effected in an electric way. The brake pedal has associated therewith a potentiometer or comparable electric position detector which generates an electric braking signal, which is provided to a brake control, in dependence on the actuation path of the brake signal. The brake control, in turn, generates an control signal for actuating the brake unit in response to the braking signal.
If the operation of the position detector fails for certain reasons a braking procedure naturally will not come about when the brake pedal is actuated. Nevertheless, for safety reasons, it has to be ensured that the driver brings the industrial truck to a fast stop. When the electric supply breaks down, e.g. because of cable rupture or the like, care can be taken in the form of an emergency current supply that there is still sufficient energy at least for the braking procedure to be initiated. However, this cannot compensate for the breakdown of a position detector.
It is the object of the invention to provide a braking device for an industrial truck including an electric braking unit in which a braking procedure can be carried out even if the position detector breaks down.